1. Field of the Invention
This invention relates broadly to an insulation system, and more particularly to an insulation system for protecting metal membrane seals in process vessels. Specifically, the insulation system is applicable to a fluid catalytic cracking unit (FCCU) of the type where a perforated grid floor in the regenerator vessel must be sealed against the interior vessel wall and any internal piping extending through the grid floor.
Some FCCU regenerators have an air distributor ring for injection of air into the vessel for burning coke deposits off of circulating catalyst. Others, of the type to which this invention relates, utilize a perforated plate or grid floor in the lower part of the regenerator. Air is passed upwardly through openings in the grid floor into the hot section of the regenerator. The grid floor must be sealed relative to the vessel wall and the standpipe or other conduits extending therethrough. Otherwise, catalyst from the hot section of the regenerator will bypass the grid floor and interfere with the operation of the unit.
The interior of an FCCU regenerator operates at high temperature, and the grid floor expands and distorts to a considerable extent between start up and operation. Because of this considerable expansion and distortion, grid floor seals have to be somewhat flexible, and thin metal membranes have been used to form the seal. These membranes must be protected from the high temperatures in the regenerator, and this invention, while applicable to insulation systems of process vessels in general, is particularly useful for a regenerator vessel in an FCCU.
2. The Prior Art
Prior art techniques for insulating grid floor seals in FCCU regenerators, while adequate to enable operation, have been subject to early failure, short run life, and frequent requirement of replacement.
The prior art techniques of insulating grid floor seals have involved covering the metal membrane seal with a substantial layer of castable refractory, sometimes with an outer layer of structurally supported erosion-resistant castable refractory. This castable material is somewhat brittle, and is subject to breaking when the grid floor expands and distorts as the unit is put into operation.
The prior art insulation system discussed above, and which is described in more detail below, is the closest known art to the present invention. No prior art search was conducted for this invention, as the very specific nature of the invention and the intimate knowledge of the inventors with existing FCCU regenerators are such that the likelihood of finding relevant published material was considered to be remote.